BASE PLATE DESIGN
230
Size of the column NPB300x150x49.3 35.5 b (1mm strip)
Factored loads: 85 mm x y
Max. compression 490.66 KN 304 375
Max. tension 228.94 KN a (1mm strip)
Max. shear 119.21 KN C/C = 100
For Compression
152
Assume the base plate size as 230 x 375 Concrete Grade, fck = 25 N/mm2
Max. compression = 490.66 kN
Base pressure = 5.69 N/mm2
< than 0.45 times the strength of bedding material
Hence O.K
gmo = 1.1 tf = 12.7 mm
fy = 250 N/mm2 a = 39 mm
fu = 410 N/mm2 b = 35.5 mm
tw = 8 mm
A = 6282 mm2
Minimum thickness check as per cl. 7.4.3
ts = √(2.5 w (a2 - 0.3 b2)gmo / fy > tf
= 8 mm
Hence, ts = 12.7 mm
Provide 16 mm
Check for weld size connecting base plate to Column
Total length availble for welding along the periphery of column fwn = fu / √3 gmw = 1.25
2x(152-12.7+304)-8 = 878.6 mm = 236.71 fwd = fwn / gmw
Deducting length 10% for end return = 790.74 mm = 189.37
Tdg = 1427.727
Capcacity of 6 mm weld = 0.803 kN/mm Tdn = 1854.446
Design force for weld = 428 kN
Required length of weld = 533.0012 mm < 790.74 mm HENCE SAFE
For Tension
Support reaction = 228.94 KN (Max Tension)
Assume 4 Nos. 24 dia H.D bolts Grade 4.6 (Bearing type bolt)
Tension capacity of bolt Tdb = Tnb / gmb (As per Cl. 10.3.5) gmb = 1.25 (As per IS 800- 2007,Table 5)
Tnb = 0.9 fub An < fyb Asb (gmb / gm0) fyb= 240 N/mm
2
fub = 400 N/mm
2
2
0.9 f ub An = 130.29 KN Shank area of the bolt(Asb)= 452.39 mm
fyb Asb (gmb/gm0)= 123.38 KN Net tensile area at the bottom of threads (An)= 361.912 mm^2
Tnb = 123.38 KN ( Approx. 80 % of Asb)
Tension capacity of single bolt Tdb = 98.7 kN
Hence tension capacity of single bolt = 98.7 kN
Tension/bolt (Tb) = 228.94/4= 57.24 kN KN
Hence provide thickness of base plate = 16 mm Hence O.K
Edge Distance
Clearence of bolt holes = 2 mm
Dia. Of Holes = 26 mm
Minimum Edge Distance = 1.5 x Dia. Of Holes (Clause 10.2.4, IS:800:2007)
= 39 mm
Maximum Edge Distance = 12tε (Clause 10.2.4, IS:800:2007)
ε = (250/fy)1/2
=1
Maximum Edge Distance = 192 mm
Edge Dist. Provided = 75 mm
Pitch Distance
Minimum Pitch Distance = 2.5 x Nominal diameter of the bolt
= 60 mm
Edge Condition : Cantilever
a1 = 35.50 mm 490.66 KN
b1 = 230.00 mm
Bending moment Md = 5.69 X 1260.25
35.5
2
= 3585.41 N-mm
Thickneaa of Plate required = √(6 Md γmo /1.2 b fy)
\ = 8.88 mm Assume b = 1
5.69
Edge Condition : Plate Supported on three sides
From Mukhanov's chart,
Ratio a/d 0.5 0.6 0.7 0.8 0.9 1 1.2 1.4 2
Plates
supported on
0.06 0.074 0.088 0.097 0.107 0.112 0.12 0.126 0.132
three sides
Interpolation
0.8 0.097
0.9 0.107
0.87 0.104
Assume thickness of stiffener = 12 a1 = 111 mm
a1 = 111 mm
d1 = 128 mm
d1=
free edge
a1/d1 = 0.87 128 mm
Hence Coefficient = 0.104 (By interpolation from chart from side)
Hence moment on the base plate Md = 9669.18 mm2
Thickness of plate required = √(6 Md γmo /1.2* b fy) As per IS 800- 2007,Clause 8.2.1.2
= 14.58 mm
Shear capacity of bolt
Vnsb = fu An / √3 = 83580 N Vdsb = 66.86 kN
Bearing capacity of the bolt:
Vnpb = 2.5 kb d t fu Kb = Min (e / 3do, p/ 3 do - 0.25, fub/fu, 1) e = 40.8
= 204672 N = 0.52 fu = 410
Vdpb = 163.74 kN do = 26 mm
fy = 250
Therefore Shear capacity of single Bolt = 66.86 KN Hence O.K
Check for combined shear and Tension:
(Vsb / Vdb)^2 + (Tb / Tdb)^2 = 0.54 Vsb = 29.8025 KN
<1 Hence O.K Tb = 57.24 KN
Design of Stiffners
Design of stiffner plate x -
Moment at the face of the column web -(for compression in the coulmn)
5.69*304/2*(230/2)^2/2 = 5719019 N-mm
Moment at face of stiffener (due to bolt tension) -
57240*100/2 = 11447000.00 N-mm
Height of plate required = √(6 Md gmo / b fy) As per IS 800- 2007,Clause 8.2.1.2
= 137.43 mm Hence, Provide stiffner plate height as 150 mm
FINAL SUMMARY
230
Dia. Of Bolt 24 mm 35.5
No. of Bolts 4 Nos. 85 mm
Thickness of Plate 16 mm 304 375
Size of Plate 230 x 375 mm
Heigh of Stiffner 150 mm C/C = 100
Thickness os stiffner plate 12 mm
152
Concrete Grade, fck = 25 N/mm2
